Filter casing



FIG. 1 is a bottom and front perspective view of my design for a filter casing showing my new design;

FIG. 2 is a top plan view;

FIG. 3 is a rear elevational view;

FIG. 4 is a right side elevation view thereof; and

FIG. 5 is a bottom plan view. 

The ornamental design for a filter casing, as shown. 